Worldwide interoperability for microwave access (WiMAX) is a new generation broadband wireless communication technology. Compared with conventional 3G access technology, WiMAX has advantages such as in high rate, quality of service (QoS), and flexibility.
FIG. 1 is a diagram of the basic network structure of a WiMAX system, which comprises functional modules including a base station (BS), an access gateway (AGW), an authenticator functional module, a paging controller, and an authentication authorization accounting (AAA) module etc. Wherein, the paging controller and authenticator functional module are generally located in the AGW, and the paging controller can be classified into anchor paging controller and relay paging controller according to its function; the interface between the BS and the AGW or paging controller is R6 interface, and the interface between the relay paging controller and the anchor paging controller is R4 interface.
Idle mode is an important power saving mode in a WiMAX system, and when a terminal is in the idle mode, it can sleep in non-monitoring time slots, so that the endurance of the mobile terminal can be increased greatly. In the idle mode, a terminal reports information of the paging group to which it currently belongs to the paging controller by various location updating mechanisms. The common location updating mechanisms generally include periodical location updating and paging group location updating. A terminal in the idle mode needs to perform downlink synchronization firstly in each monitoring interval, and during the downlink synchronization, the terminal needs to scan a downlink channel description (DCD) message. According to the description in the WiMAX protocol, if the paging group list in the DCD message does not include the paging group to which the terminal currently belongs, the terminal considers that it has moved across paging groups, and triggers a location updating flow to report the latest paging group location information to the paging controller. When downlink data addressed to the terminal is sent to the AGW, the AGW instructs the anchor paging controller to perform paging, and the anchor paging controller may instruct, via a relay paging controller, all or part of the BSs in the paging group to which the terminal belongs send a paging broadcast message to the terminal, so as to instruct the terminal to receive the data upon exiting from the idle mode.
A flow of a terminal entering the idle mode, paging, and exiting from the idle mode is specified in detail in a standard of phase 3 by a network working group (NWG) subordinate to the WiMAX forum. According the description in the WiMAX protocol, for a terminal in mobile state, the paging controller may initiate a paging according to information of the paging group to which the terminal belongs reported by location updating.
FIG. 2 is a schematic diagram illustrating movement of a terminal in idle mode in a WiMAX system. BS1, BS2, and BS3 are managed by a paging controller, where BS1 belongs to paging group 1, BS3 belongs to paging group 2, and BS2 belongs to paging group 1 and paging group 2. The terminal enters the idle mode at BS1, and chooses paging group 1 as its current paging group. When the terminal moves from the coverage of BS1 to the coverage of BS2, location updating triggered by paging area updating will not be performed since BS2 also belongs to paging group 1; when the terminal moves swiftly from the coverage of BS2 to the coverage of BS3, the terminal under the new BS3 needs to firstly perform downlink synchronization, receive a DCD message, detect that it has moved across paging groups, and accordingly initiate a location updating flow. If paging of the terminal happens before the terminal performs the new location updating flow successfully, there will be a first time paging failure for the terminal, and the paging controller has to page the terminal by a subsequent paging retransmission message. In the worst case, if the paging controller has not received a location updating message from the terminal before paging times are depleted, paging of the terminal will fail.